Fluid compressor unit



June 9, 1953 J. LE VALLEY 2,641,405

' FLUID COMPRESSOR UNIT Filed April 14, 1948 2 Sheets-Sheet 1 lza INVENTOR .aouu VALLEY 23 m;- H .5.

HIS ATTORNEY.

June 9, 1953 J. LE VALLEY 2,641,405

FLUID COMPRESSOR UNIT Filed April 14, 1948 2 Sheets-Sheet 2 JOHN LE VALLEY HIS ATTORNEY.

Patented June 9, 1953 FLUID COMPRESSOR UNIT John Le Valley, Painted Post, N. Y., assignor to Ingersoll-Rand Company, New York, N. Y., a corporation of New Jersey Application April 14, 1943, Serial No. 21,026

This invention relates to compressor units, and more particularly to a fluid compressor unit of the portable type.

It is one object of the invention to minimize the development of heat in the compressor.

Another object is to obviate leakage of fluid medium across the cooperating surfaces of the vanes and the surfaces defining the bounding surfaces of the compression chambers of the compressor.

Further objects will be in part obvious and in part pointed out hereinafter.

In the drawings accompanying this specification and in which similar reference numerals refer to similar parts,

Figure 1 is a side elevation of a fluid compressor unit constructed and arranged in accordance with the practice of the invention,

Figure 2 is a longitudinal elevation, in section, of the fluid compressor of the unit,

Figure 3 is an enlarged fragmentary side view of the low pressure cylinder of the compressor,

Figures 4, 5 and 6 are transverse views taken through Figure 2 on the lines 4-4l, 5-5 and G'--6, respectively, and looking in the direction indicated by the arrows, I

Figure 7 is an enlarged view, in elevation, partly broken away, of a container serving as a reservoir for coolant and as a receiver for the final discharge output of the compressor and having a strainer superimposed thereon for filte'rin-g the coolant from the pressure fluid stream, and

Figure 8 is an elevation, partly broken away and somewhat enlarged, of a detail.

Referring more particularly to the drav'lings, 20 designates, in general, a fluid compressor unit which is mounted upon a frame 2! having Wheels 22 to enable the unit it to be conveniently transported from place to place.

In the form of the invention shown, the compressor unit includes a compressor 23 of the retary vane-type shown disposed end'wise of the mounting 21 in tandem with an internal combustion engine 2%, whereby it driven, and has low and high pressure cylinders 25 and 26 positioned in end to end relation with respect to each ctherj The cylinders 25 and 26 have cylindrical bores 2-? and 28, respectively, for the accommodation of rotors 29 and 30, and in said rotors are radially extending slots 3i and 32 having, respectively, vanes 33 and 3'4 sli'dabl'e therein to divide the bores 21' and 28 into compression chambers 35 The vanes 3-3 and 34 are provided on 9 Claims. (01. 230-158) 2 their leading surfaces with grooves 31 that extend from their outer to the inner edges to admit fluid medium beneath the vanes 33 and 34' for preventing the entrapment of fluid in the slots and to assure adequate lubrication of their surfaces and those of the vanes.

As a preferred arrangement, the bores 21 and '28 are located abaxially with respect to each other in the horizontal plane of the rotors. The rotors, on the other hand, are arranged coaxially with each other and the portions 38 and 39 of the bores 21 and 28 Wherewith the rotors 29 and 30 have sea-ling engagement, are described. on radii equal to those of the rotors plus running clearance and are of an extent approximately equal to the space between adjacent vanes.

Closures are provided for the inner ends of the bores 21' and 28 in the form of cylindrical plates 40 that seat flush against the ends of the cylinders and are pressed thereagainst by heads M and 42 which are, respectively, secured to the ends of the cylinders 25 and. 26 by bolts 43. In order to preclude leakage of fluid along the cooperating surfaces of the plates 40 and the ends of the cylinders and at the same time minimize the use of sealing members in the assembly, the plates. Ml are disposed within cylindrical skirts 44 at the outer ends of the heads. M and 42. These skirts 44 also encircle the adjacent cylinder ends 45 which have packing members 45 arranged in their peripheral surfaces for sealing engagement with the inner surfaces.- of the skirts M.

By reason of this arrangement, only one packing member is required at each cylinder end to preclude the leakage of fluid along the cooperating surfaces of the plates 40 and the cylinders and the inner heads to the atmosphere. A sealing member 4''! isinter-posed between the heads M and 42 at their outer marginal portions, and the heads are secured together by bolts 41% extending throughv flanges 49 on the peripheries of the heads.

Similar closures are provided for the outer ends of the cylinders, that for the: bore 21. being designated 50 and the one for the bore 28- being designated it. The latter plate lies within a skirt portion 52 of a. head 53 which is clamped against the plate, 51 and the plate, in turn, is

clamped against the outer end of the cylinder 2.6 by bolts 54 A sealing ring Mi in the periphery of the end 55. of the cylinder lying within the skirt 5% engages the inner surface oi; the ski-rt to preclude the leakage of fluid from the outer end of the bore 28 to the atmosphere.

A sealing ring 46 performs a like function at the outer end of the cylinder 25. It encircles the end portion 56 of the cylinder 25 and is in sealing engagement with the inn-er surface of a skirt portion 57 carried by a head 58 bearing against the outer surface of the plate 59. The plate and the head 58 are fastened to the cylinder 25 by bolts 59 which also secure the adjacent end portion 69 of the casing of the engine 24 to the low pressure cylinder 25. Thecasing 69 is held coaxial with the compressor by an introverted flange 6I on the casing and a cylindrical boss 62 on the head 58 lying within the flange 6|. 1

The head 58 is hollow having a bore 93, and a shaft portion 64 on the rotor extends through. the bore for connection with the crankshaft (not shown) of the engine 24. 65 of the bore 63 is enlarged for the accommodation of an anti-friction bearing 66 the outer race 61 of which seats at one end against the plate 59, and an annular plate 68 is pressed against its opposite end by screws 69 threaded into the head 58 for holding the outer race 67 fixedly in position.

An additional function of the anti-friction bearing 66, apart from acting as a support for the rotor 29, is that of holding the rotor against axial movement. The inner race 19 of the bearing is accordingly attached fixedly to the shaft portion 64. It encircles the shaft portion in the usual manner and abuts, at one end, an annular spacer II that encircles the shaft portion 64 and seats against the end of the rotor 29. A nut I2 threaded onto the free end of the shaft presses the inner race 19 fixedly against the spacer II and the spacer 1|, in turn, fixedly against the end of the rotor. The width of the spacer exceeds the width of the plate 59 by the sum of the clearances required at the ends of the rotor, and these clearances Will remain as initially established for the reason that the outer race 61 is held immovable axially and the inner race 19 is restrained against such movement by the antifriction members of the bearing.

7 The outer portion I3 of the bore 63 is covered by a plate M secured to the end of the head 58 by screws and having a hole 16 to permit the shaft portion 64 to extend therethrough.

The hole I6 contains an annular member I1 having a radial flange 18 at its inner end to overlie a packing ring I9 seated in the inner surface of the plate I4. Leakage along the shaft 64 is also prevented by the inner end of the 'member I! which constitutes a sealing surface '89 and cooperates with a sealing ring 8| on the shaft 64. The sealing ring BI is rotatable with the shaft and is urged into sealing engagement with the sealing surface 89 by a spring 92 encircling the shaft 64 and bearing against the nut I2.

The rotor 39 is held against endwise movement in the same manner as the rotor 29. The antifriction bearing 83 for the shaft portion 84 of the rotor has its outer race 85 clamped fixedly against the side of the plate 5I by a ring 86 seating against the race 85, and screws 8'! in the head 53 bearing against the ring 86. The inner race 88 of the bearing 83 also seats against a spacer '89 which determines the clearances at the ends of the rotor 39 and, with the inner race 88, is

secured fixedly to the shaft by a nut 99.

As will be apparent, by providing the cylinders ofthe compressor with individual inner heads The inmost portion 4I42 and securing them together in the manner described, the several stages may be conveniently separated from each other for the purpose of inspection and repairs, if required. It is, accordingly, desirable that the rotors be also readily detachable from each other. To this end the inner shaft portions 9| and 92 of the rotors 29-39, respectively, are provided with clutch members 93 that are slidably interlocked with each other, so that each can be readily disengaged from the other, and serve to transmit rotary motion from the rotor 29 to the rotor 39.

Suitable clearances 94 may be provided between theopposed end surfaces of the shaft extensions 9I and 92 since, owing to the manner in which the rotors are held against endwise movement by the anti-friction bearings 82 and 83,

I it is not essential that the inner ends of the j: rotors abut each other to hold them against relative endwise movement.

The'shaft portions 9I92 are also supported by anti-friction bearings designated 95. These bearings are disposed in bores 96 in'the heads 4| and 42 and bear at their outer ends against the adjacent plates 49. They are suitably spaced with respect to each other to accommodate therebetween a ring 91 that has a close fit within the opposed ends of the bores 96 to assure the correct axial relationship of the bearings and thereby maintain the rotors in coaxial alignment.

The inlet ports 98 through which the fluid medium enters the initial stage cylinder are arranged in rows extending endwise along the upper side of the cylinder 25, and on the side of said cylinder are discharge ports 99 that-open into a, manifold I99 which communicates through ports I9I in the plate 49 and the head M with a low point of a chamber I92 in the opposed surfaces of the heads M 42. The chamber I92 is of annular shape, being defined by recesses in the opposed surfaces of the heads M and 92, and communicates, through ports I93 in the head 62 and the adjacent plate 49, with a partly annular chamber I94 in the cylinder 25 beneath the bore 28, and communication between the chamber I94 and the adjacent side of the bore 23 is afforded through ports I95 in the cylinder. The fluid discharged from the high pressure cylinder passes therefrom through discharge ports I96 and through a conduit I9! leading to a container I99 secured upon the fram 2|, immediately adjacent the rearward end of the compressor.

The fluid medium intended to be compressed passes to the compressor through a casing I99 which is seated upon the cylinder 25 and has an inlet conduit II9 provided with-a suitable filter I II for preventing the entrance of solids into the compressor. The conduit II9 opens into a chamber II2 wherewith the inlet ports 98 communicate, and its outlet end II3 is controlled .by a valve H4 in the form of a plate which is suspended from a, pivot I I5 so positioned that the .valve will normally tend to overlie the outlet end II 3, for closing it, but will be readily swung away and held unseated by the current of .fluid flowing into the chamber I I 2.

To the end that the valve H4 maybe forcibly placed and held in its closed position, as when the discharge pressure reaches a certain prede- 1t0n II9 that is reciprocable in a cylinder II1 sev oured to the casing I99 by bolts H8. The piston H6 lies'coaxial with the outlet. II3 and is normally held outof engagement with the valve. by a spring II9 interposed between the piston and the bottom of the cylinder .1.

The piston IIB carries an extension I20 that moves through an opening I2I in the bottom of the cylinder M1 for engagement with the valve H4. The bolts I I8 securing the cylinder I11 to the casing I09 also serve to secure a plate I22 against the outer end of the cylinder, and a conduit I23 is threaded to said plate for conveying pressure fluid at the final discharge pressure to the piston [I6 from a suitable source, as for example, the container I98. The flow of fluid through the conduit I23 may be controlled-by any suitable device (not shown) capable 'of effecting its controlling functions in response to predetermined maximum and minimum pressures within the container I 98.

Means are provided for introducing pre-cooled oil into the compression chambers 35 and 36. f or cooling thefluid during compression and to cool and lubricate the surfaces of the rotors and the cylinders as well as the anti-friction bearings supporting the rotors. To these ends the cylinders 25 and 26 are provided with orifices I24 and I25, respectively, from which the oil issues in the form of a mist into the zones of maximum clearance between the rotors and the wallslof the bores 21 and 28.

The orifices I24 are arranged in a row along the length of one side of the low pressure cylinder 25 and one orifice I25 is indicated on the opposite side of the high pressure cylinder 26. Any suitable number of orifices may be pro vided to assure the desired cooling effect and the delivery of an ample supply of oil to the antifriction bearings which flows, in the present instance, fromthe ends of the bores through the apertures I26 in the plates 49, 50 and through which the shaft portions or the rotors extend,

these apertures being sufficiently larger than the shafts to provide the necessary flow areas. The clearances thus provided communicate, through recesses I21 in. the outer surfaces of the end plates, with the'spaces I28 between the inner and outer races of the bearings.

' The supply of oil I29 used for this purpose is stored in the container I98. It is, therefore, subjected to the final discharge pressure of the compressor and is conveyed'from the container by a conduit I311 leading to the lower v.end jot.v a vertical coolerv I3I at the front end of the frame 2t and closely adjacent the radiator I32 containing the cooling water for the engine 24. Owing to this arrangement,'the air circulated by the engine fan I 33 normally provided for cooling the water for the engine will also be circulated over the surfaces of the cooler I3I for cooling the oil flowing. to the compressor. The cooler I3I is shown as being of approx imately the same height as the radiator I32. Its upper or outlet end lies at a higher elevation than the oil level in the container I93 so that the oil will normally tend to drain from. the cooler back to the container and is connected to a continuation of the conduit I33 extending to the compressor 23 and having branchesyI-34 leading to the orifices I24 and I25. In this connection'it should be explained, moreover,-, that owing to the fact that the container W9 is in constant communication with the compressor, through the conduit IE1, it is essential that the oil in the system be of such volume as to preclude the rising of its level within the container 6 tothe. height :of the "conduit II 91 in: order to" pro-- In order to eifect the removal of oil from the compressed fluid a strainer I35 is disposed over the discharge opening I36 of the container I08. The discharge opening I36 is located at the top of the container .and opens into the casing I31 of the strainer to deliver the oil-laden compressed fluid to a series of discs I38 of suitable filtering material arranged in face-to-face relation'throughout the major portion of the casing I31 but terminating near the free end of the casing I31 to define a spaced I39 therein for the reception of oil-free compressed fluid.

The discs I38 are'held in the assembled position within the casing I31 by a conduit I40 that extends axially of the discs to convey the compressed fluid from the space I39. The conduit I49 has a flange I4I at-on end to overlie the adjacent disc I38 and is threaded at its other end into a boss I42 in the casing I31 to hold the opposite end member of the disc assembly against an extension I43 of the portion I44 of the casing defining the passage I45 through which the fluid flows from the container. I98 to the filter. The conduit I40 constitutes a portion of the discharge line for conveying the filtered pressure fluid from the strainerand communicates with a main discharge conduit I46 also threadedly connected to the boss I42.

Any of the oil filtered from the compressed fluid that may find its way along the bottom of the casing I31 to the space I39 is returned to the container I98 by a conduit I41. This conduit leads from the bottom of the space I39 to the lowermost portion of the container I09. Owing to this arrangement, the difference in the static heads of the oil in the conduit I41 and.

the container I98 will be suificient to assure the return of oil from the space I39 to the container, even though the pressure existing within the space I39 may be ofa slightly lower value than that in the container I98, a condition that may be brought about by the slight resistance afforded by the filtering discs I38 to the passage of compressed fluid therethrough.

' Preferably, a check valve I458 is arranged in the conduit I41 to prevent the injection of oil from the container through the conduit I41 into the space I39 by, the pressure of the compressed fluid within the container.

Inasmuch as the oil is delivered to the compression chambers, and thus to the bearings, by the pressure existing within the container I08 it is essential that means be provided to assure the immediate creation of a pressure therein capable of promptly inducing oil flow when starting the compressor against an empty system,

' otherwise the bearings may become seriously damaged. In furtherance of this end, the dis* charge line of the container I98, in the present instance the outlet and of the conduit I49, is in the form of an orifice M9 through which the oilfree fluid passes from the conduit I49 to the discharge conduit I46.-

The restriction imposed upon the pressure fluid by the orifice I49 need be of only small de- K gree to assure a moderate pressure within the container capable of causing the: circulation 'of" oil through the cooler I 3I and the associated conduits to the compression chambers; whence it will be delivered to the anti-friction bearings. In actual practice it has been found that a pressure of approximately eight pounds at'little or no discharge of fluid through the dischargeline I 48 is ample for forcing the oil through the system when the engine is accelerating to the "normal speed, and that an orifice capable of producing this result will cause only a negligible pressure drop when the compressor is operating at the normal rate. t

In the operation of the device, the fluid medium intended to be .compressed and entering the low pressure cylinder through the inlet conduit lIIl and associated channels, passes through the exhaust ports 99 into the manifold I00, thence through the ports IN, the annular chamber I02, the ports I03 into the chamber I04 and through the ports I05 into the high pressure cylinder. There itis compressed to a higher value and discharged through the conduit I0! into the con'-' tainer I 08.

' During this initial starting of the compressor;

and while it is accelerating to normal speed, the resistance to flow of pressure fluid through the discharge conduit I46 aflorded by the orifice I49 causes the prompt building up of a pressure within thecontainer I08 capable of forcingoil from the container I08 through the conduit I30, the cooler I3I, the branches I34 and the orifices I24 and I25 into the compression chambers of both the low. and high pressure cylinders. A' portion of this oil will immediately findits way from the compression chambers through. the apertures I26 to the cooperating surfaces of the: anti-friction bearings supporting, the rotors.

' The surfaces of the elements defining the-come: pression chambers and 3B, aswell as the surfaces of the slidable vanes 33 and 34 and those of the slotsguiding them, will also be adequately lubricated so that no undue wear willbe occasioned thereto. Thereafter, whenthe compres-J sor reaches normal speed the higher pressure within the container I08 will continue to impel oil from the container and associated channels through the orifices I24 and I25 into the. com-- pression chambers in'the form'of a mist. "The; oil will be carried in that form by the compressed fluid through the channels connectingithe .dis-z' charge manifold of the low pressure cylinder: with the high pressure cylinder-and, owing-t. to the "arrangement of these passages and theI fa'ct that the fluid discharged by the-low pressure cylinder remains in motion after being discharged from the low pressure cylinder,'.little or 'no oil will precipitate to collect as a liquid andbe car ried into the high pressure cylinder in that form. Additional cooling oil is, of course," injected into the fluid medium in the compression chambers 36 and discharged, along with that previously entrained in the compressed fluid, through the conduit I01 into the container I08, whence it is carried by the compressed fluid through the passage I into the strainer I35. There, in passing through the filtering discs I38, the com-- pressed fluid is freed of oil by the time it reaches the space I 39. It then flows through the conduit I40, the orifice I49 and the discharge conduit I40 to the point of utilization or storage (not shown). Such oil as may precipitate through the filtering discs to the bottom of the strainer and find its way into the space I39 will drain through the conduit I41 into the bottom of the container I083 v of forcing oil into the cylinders The processes of spraying oil into the. compression chambers and fllt'ering'ithe 'oilvapor from: the compressed fluid .will continue throughout the entire operating period of the compressor and whenever the compressor is brought to rest, and in which case the slidable vanes 33 and 34 will recede in their guide slots, pressure-fluidwill flow from the container I08 into the cylinders and the associated channels including the chamber II2 where it will act against the valve I I4 and hold said valve in its closed position. The pressure fluid thus present within the compression chambers will equal that actin upon the oil I29 and will preclude the further injection of oil into the compression chambers.

If, on the other hand, the compressor is merely unloaded during operation, as by causing the piston II 6 to move into engagement with the valve H4 and hold said valve in its closed position, the pressure fluid within the container 108 Will continue to inject oil into the compression chambers. This is highly desirable since the first stage compressor then works at a high compres sion ratio which results in extremely high tern,- peratures so that cooling is even more necessary than when the compressor is fully loaded. a

I claim:

1. In a fluid compressor unit, low and high pressure cylinders arranged in end to end relation with respect to each other and each having inner. and outer endheads, inlet and discharge passages forthe cylinders, rotors in the cylin,- ders for compressing fluid therein, means for introducing a cooling fluid into the fluid tobel compressed in the cylinders, a chamber in the, opposed surfaces of the inner heads to receivethe cooling and compressed fluids from the lowpressure cylinder and constituting a supply chamber-for the high pressure cylinder; a container for cooling fluidto receive the cooling and compressed fluids discharged by the highpressure cylinderand having a discharge conduit, a conduit for conveying cooling fluid from the container to the cooling fluid introducing,-

. means, and means in the discharge conduit forstraining the cooling fluid from the compressedfluid flowing 'therethrough.

2'. In a fluid compressor unit, a compressor havingilow .and high pressure cylinders and in-,

1 let andoutlet passages for the cylinders, rotors:

in the cylinders, bearings for the rotors, .a' container for oil to receive the discharge. output or the 'high pressurecylinder, a discharge conduitfor the'passage of pressure fluid from the con-.

- tainer; conduit means" for conveying .oil from the container to the cylinders. at the pressure existingin the container for cooling the fluid in: the. cylinders 'and for lubricating the bearings, and means in the discharge conduit for restricting the flow of pressure fluid from the container to assure a pressure therein of a value capable during the start--v ing period of the compressor. i 3. In a fluid compressor unit, a compressor having low and high pressure cylinders and in let and outlet passages for the cylinders, rotors in the cylinders, bearings for the rotors, a con tainer for oil to receive the discharge output of the high pressure cylinder, a discharge conduit; for the passage of-pressure fluid from the container, conduit means for conveying oil from the container to the cylinders at the pressure existing in the container for cooling the fluid in the cylinders and for lubricating the bearings, and an orifice in the. discharg'econduit forrestrictj ing the flow of pressure fluid from the container to assure a pressure therein of a value capable of forcing oil into the cylinders during the startin period of the compressor.

4. In a fluid compressor unit, a compressor having low and high pressure cylinders and inlet and discharge passages for the cylinders, rotors in the cylinders for compressing fluid therein, a container for oil to receive the discharge output of the high pressure cylinder and having a discharge conduit, conduit means connected between the cylinders and said container for conveying oil from the container to the cylinders for cooling the fluid therein, a strainer in the discharge conduit for straining oil from the pressure fluid and being located at a higher elevation than the oi1 in the container, and a conduit leading from the strainer to the container for returning thereto oil filtered from the pressure fluid by the strainer.

5. In a fluid compressor unit, a compressor having low and high pressure cylinders and inlet and discharge passages for the cylinders, rotors in the cylinders for compressing fluid therein, a container for oil to receive the discharge output Of the high pressure cylinder, means communicating the interior of the cylinders with said container at a point below the liquid level therein, an outlet at the top of said container for the passage of pressure fluid and entrained oil from the container, a strainer superposed upon the container to receive the pressure fluid flowing through the outlet opening and to strain 011 from such pressure fluid, and a conduit leading from the strainer to a low point in the container for the oil filtered from the pressure fluid by the strainer.

6. In a fluid compressor unit, a compressor having low and high pressure cylinders and inlet and discharge passages for the cylinders, rotors in the cylinders for compressing fluid therein, means for introducing oil into the cylinders for cooling the fluid being compressed, a container for oil to receive the compressed fluid and entrained oil from the high pressure cylinder and having an outlet opening at the top thereof, conduit means for conveying oil from the container to the oil introducing means, a strainer above the container to receive the pressure fluid flowing through the outlet opening and to strain oil from such pressure fluid, a conduit leading from. the strainer to a low point in the container for conveying thereto by gravity flow the oil filtered from the pressure fiuid by the strainer, a conduit for conveying pressure fluid from the strainer, and an orifice in the last-mentioned conduit for restricting the flow of pressure fluid from the container to assure a pressure therein of a value capable of forcing oil through the oil introducing means into the cylinders during the starting period of the compressor.

7. In a fluid compressor unit, a compressor having low and high pressure cylinders arranged in end to end relation with respect to each other and having inlet and discharge passages, heads for the cylinders, rotors in the cylinders for compressing fluid therein, inner and outer shaft portions on the rotors, means on the inner shaft portions slidably interlocked with each other for transmitting rotary motion from one rotor to another, antifriction hearings on the outer shaft portions having inner and outer races, spacers interposed between the rotors and the inner races, means on the shaft for clamping the inner races firmly against the spacers and the spacers against the rotors, and means for clamping the outer races fixedly against the outer heads to prevent longitudinal movement of the rotors.

8. In a fluid compressor unit, a compressor having low and high pressure cylinders arranged in end to end relation with respect to each other and having inlet and discharge passages, heads for the cylinders, rotors in the cylinders for compressing fiuid therein, inner and outer shaft portions on the rotors, means on the inner shaft portions slidably interlocked with each other for transmitting rotary motion from one rotor to another, antifriction bearings on the outer shaft portions having inner and outer races, means for holding the inner races fixedly upon the outer portions of the shaft in spaced relation with respect to the rotors, and means for clamping the outer races fixedly against the outer heads to prevent longitudinal movement of the rotors.

9. In a fluid compressor unit, a compressor having low and high pressure cylinders arranged in end to end relation with respect to each other and having inlet and discharge passages, rotors in the cylinders having inner and outer shaft portions, means on the inner shaft portions slidably interlocked with each other for transmitting rotary motion from one rotor to another, heads for the outer ends of the cylinders having cavities to receive the outer shaft portions, walls in the heads between the cavities and the cylinders having apertures to permit the outer portions to extend therethrough into the cavities, spacers on the shaft portions lying within the cavities and exceeding the walls in width in the sum of the clearances at the ends of the associated rotor, anti-friction bearings on the shaft portions lying Within the cavities having inner and outer races, means on the shaft for clamping the inner races firmly against the spacers and the spacers firmly against the rotors, and means for clamping the outer races firmly against the Walls to prevent longitudinal movement of the rotors.

JOHN LE VALLEY.

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